Vibratory flexible silencers



Nov. 11, 1958 H. s. HOFFAR VIBRATORY FLEXIBLE SILENCERS Filed July 22, 1955 INVENTOR.

HEA/eYJY 110F542 a iwzm United States Paten -Q VIBRATORY FLEXIBLE SILENCERS Henry S. Hotfar, Sidney, British Columbia, Canada Application July 22, 1955, Serial No. 523,834

6 Claims. (Cl. 181-49) This invention relates to silencers of the type which are particularly useful in the exhausts of marine engines and stationary industrial engines.

A principal object of the invention is to Provide such a silencer which would be exceptionally effective in reducing exhaust noise while producing minimum back pressure and a back pressure which will not be substantially higher at high engine speeds than at low engine speeds.

A further object is to construct such a silencer of sound-absorptive, non-corrosive material which is highly resistant to deterioration by oil and acid. Such material also eliminates problems of differential heat expansion between the exhaust pipe and silencer.

Another object is to provide a silencer having the aforementioned advantages which, for the size of engine with which it is used, is small andcompact and can be mounted unobtrusively.

An object is to provide such a silencer which can be manufactured economically because no close manufacturing tolerances are required, the material used is inexpensive, and the silencer can be manufactured in quantity by an economical molding process. Such a silencer can also be installed easily because it is constructed of material enabling a hole of the desired size for connection of an exhaust pipe to be cut in it, and the silencer is sufficiently deformable so that it can interconnect exhaust pipe portions which are somewhat ohset or misaligned, or can be attached to an exhaust pipe in misaligned attitude. The silencer can be supplied in a large selection of sizes and shapes most adaptable t various types of installations.

A further object is to provide such a silencer which is light in weight so that it can be handled easily, cannot be dented or damaged readily, and requires a minimum of maintenance. The material of which it is made is reasonably heat-resistant, and the construction of the silencer preferably'is such as to reduce the access of corrosive salt air to the engine when used in a marine installation. While cooling water is discharged through marine engine exhausts, the present silencer cannot be damaged by water freezing in it in cold weather, even though the silencer may be installed intentionally or inadvertently so that water does not drain completely from it.

These objects can be accomplished by a silencer made of elastomer material such as neoprene, pliable resilient plastic, or similar materials. The silencer is composed of a hollow body which receives the exhaust gas and includes a pliable resilient slit damper wall against which the exhaust gas impinges, to flutter the wall and spread the slit for damping the pulsations of the gas as it passes through the slit, for discharge from the silencer with relatively little noise. Such slit damper wall may be a partition wall within the hollow body composed of damper flaps, or the discharge end wall of the body, or both, or a plurality of such slit damper walls may form 2,859,830 Patented Nov. 11,1958

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2 partitions within the hollow body, dividing it into compartments. Representative types of silencer incorporating the present invention are shown in the accompanying drawings." v

Figure l is a longitudinal sectional view through one form of silencer taken on line 11.of;.Figure 2, and Figure 2 is a transverse sectional view through such silencer on line 2-2 of Figure 1.

Figure 3 is a top perspective view of a different type, of silencer, parts being broken away to show internal structure.

Figure 4 is an end elevation view of another modification of the silencer, and Figure 5 is a longitudinal sectional view through this type of silencer taken on line 5--5 of Figure 4.

The silencer of the present invention may be of either the surface mounted type as represented by the form of Figures 1 and 2, and the modification of Figures 4 and 5, or it may be of the exhaust-conduit-mounted type such as shown in Figure 3. In either case the silencer includes a hollow body incorporating a longitudinal wall extending generally parallel to the direction of flow of exhaust gas through the body, an entering end wall, a discharge end wall, and, if desired, one or more internal partition walls, such end walls and partition walls being disposed transversely of the longitudinal wall and the direction of flow of exhaust gas through the body.

At least one of the transverse walls other than the entering end wall is a damper wall and has a slit extending through it, preferably diametrally, and is formed of pliable resilient material which preferably is an elastomer such as neoprene, or a pliable resilient plasticmaterial which is resistant to deterioration by oil and acid. While it is only essential that the slit damper wall be made of such sound absorptive pliable resilient material, it is desirable for the entire silencer to be made of such material and, in fact, definite advantages are achieved by constructing the silencer of elastomer material, even though its construction does not include a slit wall of pliable resilient material, because of the sound-absorbing capability of elastomer material.

The silencer of Figures 1 and 2 includes the longitudinal wall which preferably is composed of two halves 1 and 10, which are complemental. Each of these Walls preferably is of semi-cylindrical shape so that when the halves are placed in edge abutment they cooperate to form a hollow cylindrical body, although the body might be of a cross-sectional shape other than circular. For ease of manufacture these longitudinal wall sections may be molded of elastomer material, and to facilitate their integration in edge-abutting relationship it is preferred that their longitudinal edges incorporate outwardly projecting flanges 11 and 12.

The entering end wall 13 and the discharge end wall 14 of the hollow body may also be formed in halves, one-half of each end wall being molded integrally with the half 1 of the longitudinal wall, and the other half of each end wall being molded integrally with the other half 10 of the longitudinal wall. In such case the diametral edges of the halves of end wall 14 may have outwardly projecting flanges 15 formed integral with the edge flanges 11 and 12 respectively of the longitudinal wall halves 1 and 10.

The silencer of Figures 1 and 2 is of the surfacemounted type and conveniently may be mounted by securing its entering end wall 13 to the surface of a bulkhead 16 which may be the transom of a boat hull. To facilitate mounting the silencer in this manner a flange 17 may be formed integrally with the entering end wall 13 projecting radially outward from it. This flange may be clamped to the bulkhead by a clamping ring 18 preferably of metal, and bolts 19 passing through such clamping ring, the flange 17 and the bulkhead 16 may be employed to draw these parts tightly together and support the silencer. Also the entering end wall 13 may be secured by adhesive to the surface of the bulkhead if desired.

The exhaust conduit 2 connected to the engine delivers exhaust gas to the silencer by projecting into the hollow body through an aperture 20 in the entering end wall. The material of whichthis wall is made can be sufliciently workable so that the installer of the silencer can without great difliculty cut in the entering end wall 13 a hole of a size to receive and fit snugly'the exhaust conduit 2 as shown in'Figure 1. While the fitof the exhaust conduit in the entering end wall of the silencer should be tight, it usually is desirable for the aperture 21 in the bulkhead through which the exhaust conduit extends to be appreciably larger than the outer periphery of the'conduit so as to afford reasonable clearance between it and the bulkhead aperture.

The type of silencer shown in Figures 1 and 2 incorporates a pliable resilient transverse slit damper wall in the form of an internal. partition within the hollow body, which is composed of complemental, substantially semicircular damper flaps 22 and 23 of a radial extent to form between themthe diametral slit 24. Cooling water ordinarily is discharged from a marine engine through the exhaust conduit 2, so that provision must be made for flow of such cooling water through the silencer. To avoid the necessity of perforating either of the damper flaps 22 and 23, they may be disposed with their diametral sides upright and be provided with corner notches 25 and 26 forming a waterway through the bottom of the partition. In order to make the flaps symmetrical to enable each flap to flex uniformly under pres sure, the upper corners also may have similar notches 27 and 28.

The exhaust gas and water passing through the, damper partition slit 24 may be discharged from the body 1, through outlet ports 29 and 30 in the halves of the longitudinal wall between the damper partition 22,23 and the discharge end wall 14. These outlet ports preferably are substantially at the bottom of the body so that water passing through the waterway of the silencer can drain out through them and exhaust gas discharged from the silencer will be directed downward.

-'It will be evident that silencers of this type can be molded easily in a variety of sizes. The silencer is molded in two generally symmetrical and complemental halves, each including a side wall half, anen'tering end wall half, a substantially semi-circular internal damper flap, and a discharge end wall half. For ease of manufacture and silencing efiiciency it is preferred that the damper flap taper in thickness from its root edge integral with the longitudinal wall to its free edge, the thickness atthe longitudinal wall being perhaps one-half inch, and the thickness at the free edge perhaps one-quarter inch. The thickness of the longitudinal wall and the two end walls may be approximately one-half inch, and the thickness of the abutting edge flanges may be one-quarter inch. Such silencer halves may be assembled by bondingtogetherthe abutting edges and flanges.

The'silencer is very effective'in reducing exhaust noise. If the walls 1 and 10 are made of pliable resilient material such as an elastomer the hollow body will be expansive and will be expanded intermittently in rhythm with the pulsations of the exhaust gas and will thus have a damping efiect on such pulsations. The exhaust gas pulsations passing through-the slit 24 between the pliable resilient damper flaps will expand the slit, opening it to a substantially expanded width, varying in degree intermittently by bending the edges of the damper flaps, causing them to flutter,-which action will damp further the pulsations of the exhaust gas.

T heexhaust gas passes lengthwise through the hollow body substantially parallel to the axis of exhaust conduit 2 and the longitudinal wall. Since the gas admitting aperture through the entering wall 13 is 'much siiiallei' than the internal cross-sectional area of the hollow body within the longitudinal wall 1, 10 the velocity of gas flow entering the silencer will be greatly retarded prior to impingement of the gas against the damper wall 22, 23. Consequently, the pulsation frequency will be decreased and the amplitude will be increased to improve the damping effect of the flutterable damping flaps 22, 23 as the gas passes through the slit 24.

In addition the slit 24 is located in a portion of the damper wall 22, 23 facing the end wall 14 of the body which is made of pliable resilient elastomer material. The slit is therefore directed for impingement against such end wall of gas flowing through the slit. The gas flowing through the slit, because of its small cross-sectional area, will be accelerated greatly so that it impinges against the wall 14 at a much higher speed than the gas flowing through the hollow silencer body on the inlet side of the damper partition. Such high velocity stream will have a greater eflect in reducing the noise than a comparatively low velocity stream as it irnpinges against the discharge end wall 14 of the body. Because this end wall is of pliable resilient material such as an elastomer, it will be set into vibration by the exhaust gas, acting to damp the exhaust gas pulsations further. The width of flanges extending diametrally of this end wall may be made broader or narrower as desired to increase or decrease the stiffness of this wall to obtain the most eflective damping action. The turbulence created by requiring the exhaust gas to turn through an angle of approximately 90 fordischarge through the outlet 'ports'29 and 30 will also aid in reducing the pulsations of the exhaust gas.

While it will be evident that the damping action of any one of these features of the silencer described will produce some reduction in the exhaust noise, the most eflfective noise reduction will be obtained by incorporating all of these features in the silencer. In its .design the location of the damper flaps lengthwise of the hollow body, the width of the slit 24, and the length to width proportions of the body may all be selected as desired to produce the greatest noise reduction. As shown in Figures 1 and 2 the slit 2.4 preferably extends over a length substantially greater than'the maximum widthof the pipe to which the hollow body 1, 10. of thesilencer is connected. The size of the silencer for a particular installation-will be selected suchthat the slit 24 and the outlet ports 29 and will not produce excessive back pressure on the engine.

The silencer shown in Figures 4 and 5 is of thesarne general type as that shownin Figures l and 2, being adapted for surface mounting. It is formed of two halves molded from pliable resilient material such as an elastomer, and the hollow body includes the longitudinal walls 4 and 40. The longitudinal wall portion 4 is molded integrally with the entering end wall portion 41, the discharge end wall portion 42, the outwardly projecting circumferential flange portion 43, the longitudinal outwardly projecting flange portions 44, and the out wardly projecting discharge end flange 45. Similarly, thelongitudinal wall portion 40 is molded integrally with the entering end wall portion 46, the discharge end wall portion 47, the mounting flange portion 48, the longitudinal flange portions 49, and the discharge end wall flange portion 50.

This type-of silencer has no internal damper partition, but the discharge end wall 42, 47 extending transversely of the general direction of flow of the exhaust gas, is of pliable resilient material and is provided with a slit 51 preferably extending diametrally of it so that it constitutes a damper wall. Such slit may be formed conveniently by molding a shallow notch in one or both of the adjacent edge portions of the end wall halves 42 and 47, as shown. The flanges 45 and 50 may be decreased in width or entirely omitted over a portion or the entire length of such slit as may be desired to impart the degree of flexibility to the slit edges most effective to damp exhaust gas pulsations.

Alternatively, one or more deep and narrow notches may be cut in corresponding positions in the edges of the end wall portions 42 and 47 to provide a slit or slits extending transversely of the edge portions of such end wall sections. The exhaust gas conduit 52 is connected to the silencer by providing or cutting in the entering end wall 41, 46 an aperture of a size to fit snugly the outer periphery of such pipe. The silencer may then be mounted in a manner similar to that previously described, such as on a bulkhead 53, which may be the transom of a boat hull. The flange 43 is secured to the surface of such bulkhead by a mounting ring 54 preferably of angle cross section, which is secured to the bulkhead by bolts 55 extending through registering apertures in the securing ring, the mounting flange 43, 48 and the bulkhead. The exhaust pipe 52 will extend through an aperture 56 in the bulkhead, which is preferably substantially larger than the exhaust conduit to afford adequate clearance.

When used in a marine installation provision is usually required for passing cooling water through the silencer, and for this purpose one or more drain holes 57 may be provided in one or both of the end wall sections 42, 47, near the bottom of the hollow body. Such' holes may be molded in the silencer sections when they are being fabricated, or may be drilled in completing manufacture of the silencer, or may be drilled in the proper location by the installer after the silencer has been installed in the manner shown in Figure 5. If. such holes are provided during manufacture of the silencer, it is important that the silencer be mounted so that the hole or holes are at the bottom of the discharge end wall, or such holes could be provided in the longitudinal wall. If the hole or holes are to be made at an appropriate location by the installer, it is immaterial whether the exhaust gas discharge slit 51 extends vertically or horizontally, or in any other direction.

The method of fabricating the silencer shown in Figures 4 and 5, including assembly of the parts, and the operation of the silencer shown in Figures 4 and 5, are much the same as described in connection with the silencer shown in Figures 1 and 2. If the longitudinal walls 4 and 40 are of pliable resilient material they will be expanded intermittently by the pulsations of the exhaust gas, and by such action will damp the exhaust gas pulsations. Similarly, if the damper end wall portions 42 and 47 are of pliable resilient material, such end wall portions will be fluttered by passage of the exhaust gas through the slit 51, thus damping the exhaust gas pulsations. While the degree of reduction in noise probably will not be as great by use of the silencer shown in Figures 4 and 5 as with that of the silencer shown in Figures 1 and 2, the construction of the silencer shown in Figures 4 and 5 is simpler, and the reduction in noise effected by this silencer may be adequate for many installations.

In Figure 3 is shown a silencer of the type intended to be mounted in an exhaust conduit line instead of being mounted on a surface as the silencers shown in Figures 1 and 2 and in Figures 4 and 5 are to be mounted. As in the silencers previously described, however,

' it is preferred that the hollow body be of molded construction and that it be made of pliable resilient material. It may be formed of separately molded halves 6 and 60, each of which preferably is of semicylindrical shape. Integral with these halves are formed coupling neck elements and end wall sections.

The silencer may be symmetrical about a central plane extending transversely of its length, and section 6 may incorporate at opposite endsthe coupling neck portions 61 and end wall portions 62. The silencer longitudinal wall half 60 may carry the complemental coupling neck parts 63 and end wall parts 64. Edge flanges 65 and 66 projecting outwardly from the body wall may be provided along the abutting edges of the two silencer halves to facilitate bonding such halves together. These flanges may be notched over the central portion of the coupling necks for the purpose of receiving a hose clamp band to secure the coupling necks tightly to exhaust pipe ends projecting into such necks.

Within the hollow body 6, 60 one or more pairs of damper flaps 67 are provided, two such pairs being shown in Figure 3. In order that these damper flaps may be molded integrally with the body sections 6, 60, they are of substantially semicircular shape, and their diametral edges are spaced apart slightly when the body sections 6, 60 are assembled in edge-abutting relationship to provide slits 68 through which exhaust gas may flow between the coupling necks at opposite ends of the body. These damper flaps are similar in construction and operation to the damper flaps discussed in connection with the silencer of Figures 1 and 2. It is preferred that such damper flaps be tapered in thickness from their root edges integral with the body wall sections to their free diametral edges.

When used in a marine installation, provision should be made for drainage of cooling water through the silencer, and to provide this capability it is preferred that the abutting edges of the body portions 6, 60 be disposed in a vertical plane. The adjacent diametral edges of damper flaps 67 and the intervening slits 68 in that case will also be upright. To facilitate flow of water through a silencer having its parts thus constructed and arranged, the coupling necks are offset relative to the hollow body so that their circles are contiguous at the bottom of the silencer to provide a linear waterway.

The damper flaps 67 have notched corners 69 at opposite ends of their diametral sides, which cooperate at the bottom of the silencer to provide adequate passage for 'flow of water past them. By notching the corners of the damper flaps at both ends of their diametral edges simi larly the deflection of such edge portions under exhaust gas pressure will be balanced. It is not necessary, however, for the coupling neck at the entering end of the silencer to be offset to the bottom of it, nor is it necessary that the slit 68 between the damper flaps extend vertically. In fact, such slits could extend in any chordal direction and an aperture forming a waterway could be provided through the bottoms of the damper flaps as required to form a waterway.

The operation of the silencer shown in Figure 3 is generally the same as that of the silencer shown in Figures 1 and 2 and of the silencer shown in Figures 4 and S. If the body is made of pliable resilient material, the slits through which the exhaust gas passes may be distended somewhat by expansion of the hollow body caused by internal pressure of the exhaust gas. Such expansion, of course, will be intermittent in synchronism with the pulsations of the exhaust gas. 'If the walls in which the slits are provided are made of pliable resilient material, such slits will be distended further by deflection of the wall portions adjacent to the slits effected by exhaust gas pressure, and such distension also will be intermittent in synchronism with fluctuations in the exhaust gas pressure as the gas pulsates.

Both the intermittent expansion of the pliably resilient body and the intermittent distension of the slit in a pliable resilient wall through which the exhaust gas passes will damp the pulsation, and consequently the noise, of the exhaust. Such noise will also be reduced by the soundabsorptive character of the elastomer material of which the silencer is made. Sue-h distension of the slit exhaust gas .passage timed with pulsations of the exhaust gas will have the further beneficial effect of minimizing the back pressure produced by the silencer for a given noise reduction. In one installation of the silencer utilizing the principles of the present invention, for example, the back pressure was fairly constant at approximately 1.2 pounds per square inch throughout the engine speed range from 600 R. P. M. to 2500 R. P. M. Usually the maximum allowable back pressure is three pounds per square inch for gasoline engines and two pounds per square inch for diesel engines. Use of synthetic rubber as the elastomer material is quite practical, particularly for water-cooled exhausts, because the temperatures reached are not excessive. in the installation mentioned the maximum temperature'reached was 165 F.

While the silencer of the present invention will undoubtedly be used principally to reduce the noise of internal combustion engine exhaust, it may be employed for other purposes, such as in the air intake of a compressor or gas turbine.

I claim as my invention:

1. An internal combustion engine exhaust gas silencer comprising a pipe for flow of pulsating gas' therethrough, and a hollow body connected to said pipe and including a damper wall of pliable resilient elastomer material spaced from said pipe, disposed generally transversely of the direction of flow of gas-through said hollow body for impingement thereagainst of gas flowing through said hollow body, and slit over a length substantially greater than the maximum width of said pipe to define thin deflectable straight opposite edge portions flutterable by passage of's'uch pulsating gas past them through said damper wall to reduce the noise of such gas.

2. An internal combustion engine exhaust gas silencer comprising a hollow body of pliable resilient elastomer material for flow of pulsating gas therethrough, including a longitudinal wall of such elastomer material, an entering end wall of such elastomer material closing one end of said longitudinal wall, disposed generally transversely of the direction of flow of gas through said hollow body and having a gas-admitting aperture therethrough of a cross-sectional area equal to a minor portion of the internal cross-sectional area of said hollow body Within said longitudinal wall transversely of the direction of flow of gas through said hollow body for retarding the velocity of the gas flow, and a damper wall of such elastomer material spaced from said entering end wall, connected to said longitudinal wall, disposed generally transversely of the direction of flow of gas flowing through said hollow body for'impingement thereagainst of gas flowing through said'hollow body and having therethrough a narrow distendable slit with deflectable edge portions" constituting opposite edges of said slit flutterable by passage of such pulsating gas past them through said damper wall to reduce the noise of such gas.

3. An internal combustion engine exhaust gas silencer comprising a'hollow body for flow of pulsating gas therethrough and including a first wall of pliable resilient y elastomer material in said hollow body disposed generally 1 transversely of the direction of flow of gas through said hollow body a'nda second wall of pliable resilient elastomer material at the discharge side of said first wall in the direction of gas flow through said' hollow body, said first wall having through a portion thereof facing said second wall a slit directed for impingement of gas flowin'g therethrough against said second wall to'reduce' the noise of such gas.

4. An internal combustion engine exhaust gas silencer comprising a hollow body for flow of pulsating gas there through and including a damper partition wall of pliable resilient elastomer material in said hollow body disposed generally transversely of the direction of How of gas through said hollow body and a second wall of pliable resilient elastomer material at the discharge side of said damper partition wall in the direction of gas flow through said hollow body, said damper partition wall having through a portion thereof facing said second wall a slit directed for impingement of gas flowing therethrough against said second wall and the opposite edge portions of said slit being flutte'rable by passage of such pulsating gas past them through said damper partition wall to reduce the noise of'such gas.

5. An internal combustion engine exhaust gas silencer comprising a hollow body for flow of pulsating engine exhaust gas therethrough, including an entering end wall having a gas-admitting aperture therethrough, and a damper wall of pliable resilient elastomer material within said hollow body beyond said entering end wall for impingement thereagainst of gas flowing through said hollow body and'having therethrough an aperture much smaller than the internal cross-sectional area of said hollow body beyond said damper wall in the direction of gas flow for retarding the flow of gas through said hollow body beyond said damper wall, and said aperture being adapted to be opened up by gas flowing therethroug'h.

6. An internal combustion engine exhaust gas silencer comprising a hollow body of pliable resilient elastomer material for flow of pulsating engine exhaust gas therethrough, having a gas admitting aperture in the wall thereof of a size equal to a minor portion of the internal crosssectional area of said hollow body, and including a damper wall of pliable resilient elastomer material for impingement thereagainst of gas flowing through said hollow body, said damper wall having a slit therethrough openable to a substantially expanded width by the force of gas flowing therethrough.

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